Abstract
The nonempirical SCF method with a STO-3G basis set is used to study the effects of the geometry (SiO and AlO bond lengths and SiOAl angles) and chemical (the Si:Al ratio) characteristics of zeolites on the vibrational frequencies of their OH groups modeled by the H3SiOHAlH3, H3SiOSi(OH)3, and H2AlOSi(OH)3 molecules. It is shown that the values of the vibrational frequencies are particularly affected by the structural characteristics (e.g., changes in the Si-O and Al-O bond lengths and the SiOAl angle of 0.04 x 10 m and 20, respectively, result in shifts of the stretching frequency nu/sub OH/ of up to 40 cm ), while the influence of the chemical composition of zeolites is negligibly small (e.g., a substitution of Al for Si in the third coordination sphere of OH leads to a change of about 1 cm ).
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